In recent years，more and more water-saving ship locks have been used as the main design scheme in various domestic pivot ship lock projects. The water-saving ship locks have the advantages of reducing working head，reducing the water consumption of locks and improving the flow conditions in the approach channel of high head locks in the mountainous river areas with high head. In this paper，taking the capacity expansion project of Bajiangkou Ship Lock as an example，in view of the problems such as selection of water-saving form，the design of main structure，the layout size，and the analysis of internal force of the structure，the structural form is determined and the key stress position of the structure is studied. The finite element calculation method is used to compare the various working conditions and the main structures，and the weakest part of the integral water-saving ship lock structure can be drawn，and further structural optimization is carried out for the position with less stress.